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Patients' postal codes can be used as an indicator of socioeconomic status for adjusting physician profiles

The health outcomes of a doctor's patients often form the basis of the physician performance profile. Physician profiles that fail to adjust for patient socioeconomic status (SES) overstate the performance of physicians who care for more affluent patients (who are more likely to have better physical and mental health) and penalize physicians who work with poorer patients (who are more likely to have worse overall health). Yet managed care and other health organizations cannot easily adjust physician profiles for patient SES because doctors do not routinely collect socioeconomic data on their patients.

An easy way around this is use of patients' ZIP codes to serve as indicators of their SES, according to a study supported by the Agency for Healthcare Research and Quality (HS09963). ZIP codes or census blocks typically correlate with income, education, occupation, and wealth, explain Kevin Fiscella, M.D., M.P.H., and Peter Franks, M.D., of the University of Rochester School of Medicine and Dentistry. They compared the effects of adjusting physician performance profiles using three different measures of patient SES: one derived by geocoding patient addresses to the census block group, one using patients' ZIP codes, and the third based on patient-reported education.

The researchers took a random sample of 100 primary care physicians in Western New York and 50 consecutive patients seen by each physician to examine the effects of these SES adjustments on physician profiles for patient satisfaction and physical and mental health, which were based on patient questionnaire responses. The effects on physician rankings for patient satisfaction using the ZIP code SES were greater than those of the other two measures, which had negligible effects.

For the physical and mental health status rankings, both ZIP code and census block measures had similar effects. Individually measured education did not yield a greater effect on physician ranking than either of the other two measures for any of the patient outcomes. These results suggest that SES derived from either patient census block group level or ZIP codes may offer a convenient alternative to individually collected SES data for adjusting physician profiles. In fact, ZIP code-derived SES may be preferable, given the loss of information associated with incomplete matching during geocoding.

Details are in "Impact of patient socioeconomic status on physician profiles: A comparison of census-derived and individual measures," by Drs. Fiscella and Franks, in Medical Care 39(1), pp. 8-14, 2001.

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